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Adaptive direct metal/material deposition process using a fuzzy logic-based controller LMD (Laser Metal Deposition) is a technique used to repair damaged components and directly form three dimensional structures. From the aspect of productivity, improvement of the shape accuracy of the deposit is required to reduce machining process after LMD. Objective of this work is to control the build-up shape by adjusting the weld pool size. Configurations of deposits made with various LMD process conditions were measured in cross section. In addition, the signal intensity of heat radiation, plume emissions and laser reflections from the weld pool was monitored by photodiodes intergrated in laser processing head during LMD process. The results showed a strong correlation between weld pool size and signal intensity of heat radiation. Adaptive shape control system, which consists of in process monitoring system and PID (Proportional-Integral-Derivative) controller using that correlation, was developed to control build-up shape. Due to the liner relationship with weld pool size, laser power was selected as the PID output parameter adjusted by the heat radiation signal. Since the target value of the heat radiation signal can be changed flexibly during the LMD process in our PID control system, deposit shape is successfully controlled as required with sufficient profile accuracy of the build-up layers. V C 2014 Laser Institute of America.

Microstructure of creep ruptured specimens is investigated in order to understand the effect of Co and B on long term creep rupture strength of 12Cr cast steels. The specimen with 2.5% Co contains no delta-ferrite and has better tensile and impact properties than Co free specimens including about 1 vol% delta-ferrite. In short-term creep rupture region, Co containing steel has shown better strength than Co free steel, while in long term region such as over 7000 h at 923K, Co free steel has shown better strength. The addition of Co promoted recovery of microstructure. The difference between 20 ppm B and 50 ppm B steels in short-term creep rupture property was not observed, while in longterm region, 50 ppm B steel has a tendency to show better strength. From ATE method, it is considered that some of B have been included in carbide such as M 23 (CB) 6 , and retarded coarsening of carbide. According to calculation of thermodynamic equilibrium, solid solution content of W and Mo was reduced by Co addition. Therefore the thermodynamic stabilization of microstructure associated with the solid solution strengthening of W and Mo has decreased and the formation of Laves phase has been enhanced. It has been concluded that improvement of stabilization and enhancement of formation of Laves phase by 2.5% Co addition is one of the reasons of the deterioration of long-term creep rupture strength.

Synopsis : Microstructure and precipitates of creep ruptured specimens were investigated in order to understand the effects of carbon (C), nitrogen (N) and nickel (Ni) on long-term creep rupture strength of 10Cr heat-resistant steels containing boron (B). The low-N steels showed higher creep rupture strength than the high-N steels. In long-term creep rupture region such as over 10,000 h at 650°C, the deterioration of creep rupture strength was not observed in the low-N, high-C steel. On the other hand, the creep rupture strength of the low-N, low-C steel dropped to the strength level of the high-N steels. The addition of N to the B containing steels promoted the recovery of microstructure. The formation of coarse BN in the high-N steels led to the decrease of the amount of effective B that dissolved in M 23 (C,B) 6 and suppressed its coarsening. From EDS analysis of precipitates, the fraction of M 23 C 6 in the low-C steels was less than that in the high-C steels, while the fraction of coarse Laves phase in the low-C steels was more than that in the high-C steels. In the low-N, low-C steel, the coarsening of precipitates caused the deterioration of the creep rupture strength after 10,000 h exposure. Ni lowered Ac1 and Ac3 transition temperature, but it did not affect the fraction of precipitates according to the calculation of thermodynamic equilibrium using Thermo-Calc. It is concluded that C and N are more effective to the stability of microstructure than Ni.

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